The present invention relates to gray-black encapsulated pigments based on zirconium silicate as the encasing substance for encapsulating pigmenting or colorant compounds in the form of a discrete phase. Further, the present invention relates to a method for making these encapsulated pigments.
Encapsulated pigments also known as inclusion pigments in general are known in the art, as for example from the German Patent 23 12 535. They consist of transparent crystals of glaze-stable substances such as zirconium silicate, zirconium oxide or tin oxide which encase or encapsulate inorganic anhydrous pigmenting or colorant compounds in a discrete phase. Pigmenting compounds are illustrated by Thenard's blue, titanium yellow and especially cadmium yellow and cadmium red. Moreover, zirconium iron rose with Fe.sub.2 O.sub.3 encased in a zirconium silicate casing also is known. The manufacture of these encapsulated pigments is carried out by methods well known in the art, e.g. heating the casing substances, or its initial precursors and the pigmenting substances to be encased, or their initial precursors, in the presence of mineralizers, to temperatures up to 1200.degree. C. However, it has been found in the art that this procedure does not allow encapsulation of all conceivable pigmenting compounds into the casing substances with significant yields.
The palette range of gray-black colors is not very wide. Essentially such pigments are obtained from iron oxides and chromium oxides, optionally in combination with other oxides such as manganese oxide, copper oxide, nickel oxide or cobalt oxide. Up to this time, no gray-black encapsulated pigments have been known.